Process of treating zinc ores.



Patented Sept. 7, 1909.

F. T. SNYDER. PROCESS OP TRBATINGZING ORES. A PPLIOATION :FILED JUNE 2s,1905.

F. T. SNYDER.

PROCESS OP TREATING ZINC ORI-IS.l

l APPLIOATION FILED JUNE 23,1905.

Patented Sept. 7, 1909.

Z SHEETS-SHEET 2.

UNITED STATES 'T UFFICE FREDERICK rr. emmen, or osx-'PARK ILLINOIS,essIGNoR, BY MEsNE ASSIGNMENTS, 'ro ELECTNIQMETALS -coMrANY, or CHICAGO,ILLINOIS, A CORPORATION or WEST VIRGINIA.

' .PROCESS or TREALFING ,zr-NC ONES'.

Specification of Letters Patent. Patented Sept.. 7., i909- Applicationfiled .T 1111023', 1905. Serial No. 266,541.

To all wil-.0m it magro-neem: -Be 1t known that l, FREDERICK torni, andis applicable particularly to sultid oresI containing both leadand zinc;By slagtorming ores, l refer to ores carrying materials .which whenroasted form` a metallic oxid such as lime, iron oXid or lead oXid inadditionl .to the zinc oxid.-

lhe ordinary method of reducing Zinc oresl consists, brieiiy, in heatingthe roasted' ore with carbon, ina retort, by means of external heat, airbeing excluded from the retort.v

Under favorable conditions the zinc is reduced and volatilized, andafterward collected andcondensed.

.Zinc ores containing any considerable amount 'of slag-formingmaterials, however, can not be commercially treated in lthis way,because the slag corrodes and eats through the walls of the retort. Thisis particularly true ot' a -basic slag containing lime with iron, which.takeslup silica from the retort. The walls of the retort arenecessarily thin to permit the 'passage of the heat to the content-s,and -so are soon destroyed by the slag. .It it :be attempted to smeltsuch. ores in a blast-furnace such as is used. in lead smelting, theoxygen ofthe blast burns the reduced and volatilized zinc to ,zinc oxid.In such caseihezinc not only can lnot berecovered,but its :presence isan actualdetriment to the smelting operation, because .theaccumulation.of .the zinc oxid, which is .practically inusible, clogs up the.furnaceand interteres .with the smelting, also 4increasing the cost forfuel- Whenorescontain 'relatively Small quantities Yofjzinc with leadand silver,'the usual practice .is to ,Smelt them in a fblast furnacefertile-.lead and silver andmake no attempt toxecovent-he zinc, .Whichtoa limited extent can xbefdissolved in the 'slag inthe form ofzinc.oxid,.and soeliminated. The :practical limit to the .amount ot zinc.which .can be slagged ott .is.ab0ut.ten.per cent. ;For.this

T. SNYDER, citizen of the United States, residing at O ak.

' stage.

ore-1s smelted` upon a slag bath iioated upon reason the fees'chargedAtor lead smelting-are always lucreased when'there is any considerablepercentage of' Zlnc present, and ores containing more than fifteenpercent. ot zinc are usually unprotitable.

A slag whichis basic in character from lime, can not be used inthe'blast-turl-iace process of leadsmeltiug, Where zinc oXid must bedisposed of, because zincoxid will not readily dissolve in suoli a slag;and as `before stated, in the zinc4 distillation-process such a slag isespecially to be avoided because it attacks the clay retorts.v

Thereare large quantitiesof lead-zinc sul-- lid ores containing, forexample, approximately thirty per cent. of zinc and teu per cent. oflead, which have. heretofore'been connnercially neglected, because ofsuch practical diiiculties in the way of successful reduction, andbecause lthe recoveryot' either metal alone lwould not pay for the costof treatment. The process ot my invention is particularly applicable tothe treatmentL ot such ores, and makes it possible to recover nearly allof both the lead and the zinc in a single smelting operation.

'In accordance with my invention, the ore havingl first been roasted toconvert the sulfids into oxids, isl mixed with fluxes such as lime andiron (unless already'present) in such proportions as when suielted toproduce a slag whichwill form at a temperature between thevolatilization temperatures ot- ZiniA and lead. This charge is tirstpreheated in the presence of the carbon to be used in smelting. so as tostart thein-oces's ot' reduction/as far as possible' and drive voit' thenoumet'allic gases, lwhile keeping the free surface of the chargesufficiently cool to prevent vaporization and loss of zinc at this Finall'y', after such preheating, thc

a molten lead electrode-in a closedjelectric furnace from wl'nch alr orother extraneous gasis eXc1uded,lthe heat- .being produced. by

electric current .passed through the slag between the molten leadelectrode and another electrode (which may be of the same kind) incontactv with.the slag; vthe residues heilig completely fused. The*metals are thus reduced, the molten lead sinkingto the bot-tom ofthefurnace while the zinc is volatilized and escapes from the body otthe charge asa gas, whchis later condensed.y An important zinc oxid andlead oxid` from dissolvin m consideration is the composition ofthecharge so that when smelted the slag will form at a ,temperature betweenthe volatilization temperatures of zinc and of lead, will possess thecharacteristics of low specific avity and high electrical resistance,and wi have practically no tendency to dissolve andretain zinc oXid. A'slag which is high in lime orother ingredient which has a chemicaltendency to displace zinc oxid in the combination will answer theserequirements. The precise composition of the slag in any case willdepend largely upon the character of the ore under treatment.

The presence of considerable quantities of lime inthe slag is desirablefor the further reason that the specific electrical resistance of theslag is thereby made high, thus providing for the effective developmentof heat when an electric current is passed through the slag. But in anycase the materials of the furnace charge should be thoroughly heatedbefore smelting so as to drive o so far as possible all gases, such ascarbon monoxid and dioxid which would tend to dilute the zinc vaporproduced in smelting. It will also be desirable to pre-heat the ore inthe presence of the carbon which is to be used in smelting, so as tostart the process of re-V duction as far as possible without the loss ofvaporized zinc, in the preliminary heating operation. The'heat whichremains in' the ore after roasting may thus be utilized to aconsiderable extent for reducing a portion of the lead and probably someof the zinc, the limit being that the vaporizedY zinc should not beliberated above the body of the ore, but condensed within and on suchbody. ln this way the preliminary heating of the ore with carbon takesadvantage of the heat which is already in theore from roasting to startthe process of reduction, and so lessens the amount of the more costlyelectrical heat required foi smelting. The carbon required for reductionof the; ore, in the form of coke or lean coal, is therefore prefer;VJably added to the hot charge in the heating chamber after the roastingis substantially completed. if only a gaseous coal is available, it canbe mixed with the ore and then heated in a reducing atmosphere until thegas is driven olf. When the process of reduction has been carried as faras possible` in the preliminary heating chamber Without loss of zincvapor, the charge is introduced into the smelting furnace and thereduction carried on in the absence of air, heatl being developed insidethe furnace by the passage of an electric current.

As an additional means of preventing the the slag, a layer ofincandescent car n should be maintained floating on the surface of themolten slagY bath; and the 'furnace charge is Yfed into ontact with this-hot carbon. Before the metallic oxids can reach the body ofthe'slag,'they are reduced by the carbon, the metallic zinc beingvolatilized and rising through the ore, while the metallic'lead, inliquid form, being insolublel in the slag, sinksthrough it and settlesin a body underneath. TheI 'carbon layer floating onthe slag also servesto support and buoyup the mass of unreduced ore, so that the volatilizedzinc can readily escape withoutpassing through the body of slag. Inmaking up the furnace charge there should be enough carbon present toprovide an excess of about ten per cent. over that which istheoretically required for the reduction of the zinc and lead oxids, theexcess goin to maintain the floating bath of car n.

coated with and entangled by the sla and carried away when the excess ofslg is tapped olf.

In dealing with ores containing both zinc and lead, Lmix the materialsof the furnace charge in such proportions as to produce a slag whichwill form at a temperature between the volatilization temperatures ofzinc and lead, that is to say, at a temperature approximately between10000 and 1100o centigrade; the materials, furthermore, beingproportioned so that the slag formed at such temperature will besubstantially saturated with an alkaline oxid, such aslime. A slagcontaining approximately 30 percent. of lime, 30 er cent. of iron oxidand 40 per cent. of silica (or theirrrespective equivalents) will havethe desired characteristics. When the furnace is continuously"`suppliedwith materials which will unibe to form such a slag, at the temperaturerequired, it is evident that when this temperature is reached, anyfurther energy supplied to the Otherwise this carbon would be graduallyfurnace in the form of heat will be expended in the reduction of the oreand formation of slag, instead of increasing the temperature of thefurnace. By properly selecting and proportioning the materials of thecharge, as above described, and keeping the furnace supplied therewith,I am therefore enabled to prevent the temperature in the furnace fromrising to a point at which the lead as well as the zinc wouldvolatilize.` The lead and zinc therefore upon being reduced will beseparated, the zinc bein vaporized, while the lead collects in liquiform below the slag, where it may be drawn off. The volatilized zinc maybe condensed in liquid form in a separate vessel. The absence of air inthe furnace makes this possible, since the reduced zinc will not beoxidized as in the blast-furnace lead smelter. In order that the zincmay be condensed in a liquid form, however, it is necessary that thezinc vapor should be, so far as possible, free from diluting ses, suchas carbon monoxid. This L is an a ditional reason for the use of analllt.

kal'ne 'oxi'd nur, siren as time replace of the limestone 'or 'calciumcar onate ordinarily used in lead snelting. y Iii the limestone 'wereused in the smeltin 3 'suil'ici'ent quantities ocarbon 'monoXid d begiven o n the process' of reduction to 'dilute the zinc va` o'r to 'an'undesirable eXtent, S0 that it. Wo'ul condense in the form ofzinc dustinet'ead 'o 'in 'the form of liquid zinc.

l. metallic lead sinking below 'the slag may bedivid'ed b' 'a bridgeWall off the furnace 'into 'tw'o -n ten electrodes Whichmay serve 'toconvey the 'electric current 'to and from 'the slag. n such caSe thelreaft is developed Aprincipally in the slag unit-ing the twoelectrodes, Which is of high electrical reeiStn'ce by reason o the'excess 'of lime or other alanine oxi'd present.. l l

Another 'feature of my invention consists in util-izi'n" the reei'drregases 'from the 'zinc condenser or heating purposes. Such fgaees willccmtein carbon monoxid, which, alter the Zinc has b e'e'n removed, maybe burned to carbon i'oxidby mixin 'with air. Tire heat produced may 'heuti ized ito assist in the roastingfof the raw ores and when this isd'one, 'the sr'nail amount 'of zin which is carried avay by S'u'c'hgases, is burned to oir-id emi returned again to the ru-mace, and sosaved. 4 y v The accompanying drawings, illustrate an elle'c'tlri'cfurnace especially designed for the practice of 'my improved process. .Yy

Figure 1 'is a 'longitudinal sectional elevation o'f the furnace; Fi 2is a View in -cross section on line '2 2 of Pig l; and Fi' 3 is a viewin cross secti'on on line 3 -3 'of i'g. 1.

The same letters of reference 'designate the same 'parts Wherever theappear.

The lower por't'i'on of t' 'e main chamber 'a olf 'the furnace isdivided by a bridgeforming two Wells a at which 'communicate by U-ehapedpassages with 'the exterior 'ofthe furnace, as shown 'in Fig. 2. Theelectric conductors c are di` ped'into the molten metal in 'the ou'terarms of 'these ll-shaped passages,-

the molten metal in Said wells a a2 serving ne electrodes connecting'with the slag 'b'ath of. Lthe furnace. lt is intended that thereshalllbe su'ilicient 'material in the furnace so that the slag will riseto 'a level somewhat higher than the 'top 'of the bridge The two moltenelectrodes 'in 'the wells a a2 will 'be' electrically uni'ted by 'thebody of slag which lies upon 't-hefbridge and 'fioats upon said moltenelectrodes a't ei'th'e'r Side of said bridge. The molten slag iselectrically cony dnctin but oi considerably 'higher resistanceft an themolten electrodes; and since the heating eiiieet of an electric currentincreases with 'the increase of resistance of 'the conductor through'which the current is passedi it will be seen 'that 'in my furnace themaximum heating eect of 'the 'current will be developed in lthe slag'at. the top Where .incandescent lcarbon floating on its Surface..

'The Ifurnace shown ie constructed with the preliminary heating orroasting chamber located above tlr'e ma in emeltingchamber a. n openingc is provided in the `reverberatory roo? of the en'relting chamberthrough which the roasted ole may be ied into Said srneiltin'g' chamber.A roof i provided immediately over the opening c 'and 'the materialeI inthe chamber f are so heaped up around the edge oi sai-d openingtlratthey reach n'p to the roo-t 'la whereby 'Said 'opening is normally-:sealed xto prevent the escape. through said opening, of gases .fromthe smelling chamber (1 lI't ie intended that theee gane/s, whichcontain the reduced and vol'atilized zinc, shall pass into a chamber 7.'where the zinc may he condensed. n Fig. 1 the condensing cha'mloersl is'Seen at one end of the furnace' comnnmicatiner with the chamber a by 4apassage m- Wlicr lea'ds over a bri'dge'wall njdivi'dln the twotchanilbers.

Fines c Z1 ead 'up llirongh lthe Wall of the lnrn'ace `and 'open intothe upper roasting chafmber "f", so -that the uncol'ide'nsed gaseeescaping tlrrmigl Said lines may be burned in said inet-'mentioned-cha'mlber to in the roasting vprrwic'-ees. A very considerable amou'n'tof 'energy is thus dl'ta-ined from the carbon momoxid being burned toli'oxid. From the roasting 4chamba the rod-not ci: combustion "nalllyescape throug a stack s.

n 'the "furnaceillustrated-` the wells a n2 communicate by U-'sharpedpassages wi'tl-i correepondirrg wells openirrg 'outside' the furn'ac'e,through Whichthe molten 'metal may be la'dled out'. Similarly, vthe'condensing chamber lle communicates' 'with the exterior oi the Ifurnaceby lJ-Shaped passages p 7j', the 'on'ter arms 'of which form throlmhwhich `the metal 'condensed in 'said chamber may be removed. Som'e lead'fapor may be carried over with the zinc into the lchamber g 'Where itwill tbe condensedz 'and will Settle at Lthe bottom cfs-aid fcharn'he'r,from which it may 'be drawn off through a passage 7).

re condensed zinc is "drawn on' through the I 'in said chamber may theoil burners are provided. for this purportion of the fines k leading tothe heating chamber f may be kept in operation during the smelting, ifdesired, to furnish additional heat forroasting. Air is admitted to theroasting chamber in order to burn the gases brought by liues c 7s fromthe lower portion of the furnace.

The operation of the furnace in carrying outr my process is as follows:The ore having rst been crushed, and it may be partially roasted, isintroduced through the door f into the chamber f Where the roasting iscompleted, and the orfJ highly heated to drive 0E all gases as faraspossible. The sultids are almost entirel converted into oxids, and theresulting su furcus gases, and the steam produced from any moisturewhich. may have been present, together with theproducts of combustion,and gases coming from the lower portion of the furnace, are all passedthrough the stack s. When the'pre-heating of the elements of the chargeis completed, the materials are fed through the opening e into thesmelting chamber, said opening then being sealed-up by the heaping up ofmaterial around it to revent the escape of the gases through it. ow bypassing an electric current of sufficient strength from one moltenelectrode to the other through the materials contained in the smeltingchamberthe required tem rature be maintaine This temperature should besuiiiciently high to volatilize zinc, but not sutlicient to volatilizelead. The materials of the furnace charge havin been selected andproportioned so as to orm a slag, saturated with lime, at thistemperatm'e, said temperature will not rise, as long as the supply ofslag-forming material is kept up, any excess of current onl increasingthe rate of smelting. The ore 1s reduced by the heated' body of carbon,`the fixed oxyten kof the metallic oxids combining with e carbon to formcarbon monoxid, leavin the metals in a free state. The metallic eadsinks through the slag and adds to the molten electrodes inthe wells aa2 this chamber is kept between such limits that the zinc is condensedin said chamber in a liquid form, from which it may be removed throu hthe well Any remaining gases, as be ore described? pass through theilues 7: into the roastin chamber f where they are burned to uccvheatrin the roasting 4 chamber. The waste products of combustion'thencepass oil through the stacks.

It is essential to the properV conduct of this process that theproduction of gaseous zinc should take place in the absence of freeoxygen, to prevent the zinc from being burnedl to oxid, and thedevelopment of the heat inside the furnace by an electric current,instead of by the burning of coke, fully meets this condition. It isvfurther essential, in order to secure proper condensation of the zinc,that the elements of the furnace charge andthe fluxes used should besuch as to produce the minimum quantity of gas during smelting.

I claim:

l. `The hereinfdescribed process of treating zinc-lead ores, in whichthe ore is smelted with carbon upon a slag bath which is lioated upon amolten lead electrode in an electric furnace from which air is excluded,electric current being passed through the slag between said moltenelectrode and a second electrode in contact with the slag, and thetemperature thereby maintained at a point between the volatilizationtemperatures of lead and zinc; whereb the ores of lead and zinc arereduced and the metals separated, the lead sinking through the slag toadd to said electrode, while the zinc vaporized and separatelycollected.

The continuous process of treating slag forming ores containing zinc andlead, which consists in pre-heating the ore with carbon to drive oli'gases and to start the process of reduction, then continuing thereduction in an electric furnace in the absence of air, at a temperaturesutiicient to volatilize the zinc without volatilizing the lead, saidore being mixed with carbon and with iron, silica and lime in suchproportions as to form a slag at said temperature, said mixture beingfed upon a bath of said slag in the furnace, an

electric current being passed through said slag to maintain saidtemperature, collecting the reduced and volatilizedzinc, removing theother products of smelting and adding further charges from time to time,including Aquantities of carbon in excess of the amount required forreduction, withoutinterrupting the operation or admitting air.

3. The continuous process oftreating slagforming ores containing zincand lead, which Y consists in mixing said ores in such proportions, withslag-forming material, as to produce a slag winch forms at atemperaturel between the volatilization temperatures of zinc and oflead, smelting said mixture with carbon in the absence of air in anelectric furnace, maintaining a supply of said mixture in said furnaceby adding fresh charges from time to time, removing the products ofsmelting while conducting the operation, whereby the metals are reducedand separated and the formation of slag from said reduction, thencontinuing the re uct-ion in an electric furnace in the absence of air,at a temperature sufficient to volatilize the zinc without volatilizingthe lead, said ore being mixed with carbon and with iron, silica andlime in such proportions as to form at said temperature a hi h limeslag, such mixture being fed upon a slag bath sufficient to maintainsaid -temperature, collectin and condensing the reduced and volatilizedzinc, removing the other products of smelting and adding fresh chargesfrom time to time, including quantities of carbon slightly in excess ofthe amount required for reduction, without interruptin the operation oradmitting air.

5. Theflierein described process of treating lead-zinc ores, whichconsists in maintaining two separate bodies of lead in molten conditionat a distance from each other to serve as electrodes, electricallyuniting said bodies of ath of said slag in the furnace, passing anelectric current through said lead by a bath of molten slag floatedthereon, gradually feedin said ore, together with carbon and an al alineoxid flux onto said slag bath in the absence of air, and passing anelectric current from one of said bodies of lead to the otherthroughsaid slag, sufficient to maintain the slag at a temperaturebetween` the volatilization temperatures of lead and zinc, the metalsbeing thereby reduced and separated, the zinc volatilizing and risingabove the bath, while the lead in a molten state sinks through the bathand joins the lead electrodes.

6. The process of smelting zinc ore, which consists in preheating suchore, smelting the preheated ore with carbon and luxe in the absenceofair by electricalheat, con ensing the zinc vapor from the gaseousproducts of reduction, and then burning the uncondensed gases over andin contact with the ore which is being preheated, whereby the metallicoxids produced in such burning are deposited on the ore and returned tothe smeltingy furnace, as described. In witness whereof, I hereuntosubscribe my name this 21st day of J une` A. D., 1905.

FREDERICK T. SNYDER. Witnesses:

DE WITT C. T ANNER, IRVING MACDONALD;

